<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title></title>
</head>
	<style>
		#box{
			width: 520px;
			height: 520px;
			background: url(img/pic.jpg);
		}

		div{
			width: 50px;
			height: 50px;
			border: 1px solid #f0f0f0;
			background: #f0f0f0;
			float: left;
		}


	</style>
<body>
	<div id="box">
		
	</div>
</body>
</html>

<script>
	var box = document.getElementById('box');
	var str = '';
	for (var i = 0; i < 100; i++) {
		str += '<div onmouseover="demo(this)"></div>'
	}
	box.innerHTML = str;

	function demo(v){
		v.style.background = 'none';
	}

</script>